The present invention relates to magnetic tape drives, and more particularly, this invention relates to attenuating reaction forces in magnetic tape drive motors.
In magnetic storage systems, magnetic transducers read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For tape storage systems, that goal has led to increasing the track and linear bit density on recording tape, and decreasing the thickness of the magnetic tape medium. However, the development of small footprint, higher performance tape drive systems has created various problems in the design of a tape head assembly for use in such systems.
In a tape drive system, the drive moves the magnetic tape over the surface of the tape head at high speed. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial and so goals in these systems are to have the recording gaps of the transducers, which are the source of the magnetic recording flux in near contact with the tape to effect writing sharp transitions, and to have the read elements in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read elements.
Brushless direct current (DC) motors are used in tape drives to induce motion of the magnetic tape over the tape head, as brushless DC motors enable high speed tape motion in a compact form factor. Moreover, brushless DC motors have desirably long lifetimes, as they do not include brush contacts which eventually wear out with use over time. Internally, brushless DC motors generally include a stationary stator that has legs which are wrapped with coil windings. The legs provide a magnetic path that couples with a sub-assembly, and is thereby able to induce a relative rotational movement between the sub-assembly and the stator. Specifically, the coupling of the magnetic paths to the magnetic field generated by the coils wrapped around the stator legs create a torque which thereby includes the rotational motion which may selectively be used to transport tape from supply reel to take-up reel, and/or vice versa. However, while a net resulting torque is being generated by the magnetic coupling effect in the motor, there are also subtle oscillations in the torque. These oscillations cause the torque waveform output by brushless DC motors to have a cyclical nature.
Moreover, because the stator is magnetically coupled to the rotor sub-assembly, the forces acted on the rotor sub-assembly by cycling the electrical current through the coils of the stator, are also acted on the stator legs themselves, and hence the stator support feature as well. Furthermore, these reaction forces are transmitted throughout the main support plate also, as the stator is rigidly coupled to the main support plate in conventional brushless DC motors. Many conventional brushless DC motors also implement a tape drive deck plate that supports both the motor itself as well as the head actuator assembly used to perform read/write operations.
Accordingly, although undesirable variations in the torque waveform are produced at the stator level, these disturbances are transmitted up to the magnetic tape head itself. The spacing between the magnetic tape head and a magnetic medium positioned thereover becomes unstable as a result of these disturbances as well, thereby negatively effecting the position error signal (PES) during operation. Again, as tape drive capacities trend toward higher capacities, the detrimental effects of these instabilities is only compounded.